When a chromite ore (A) is fused with sodium carbonate in free excess of air and the product is dissolved in water, a yellow solution of compound (B) is obtained. After treatment of this yellow solution with sulphuric acid, compound (C) can be crystallised from the solution. When compound (C) is treated with KCl solution, orange crystals of compound (D) crystallise out. Identify compounds A to D and also explain the reactions.
OR
An oxide of mangnese (A) is fused with KOH in the presence of an oxidizing agent and dissolved in water. A dark green solution of compound (B) is obtained. Compound (B) disproportionates in neutral or acidic solution to give purple compound (C). Alkaline solution of (C) oxidises potassium iodide solution to a compound (D) and compound (A) is also formed. Identify compounds A to D and also explain the reactions involved.
A is FeCr2O4, B is Na2CrO4, C is Na2Cr2O7.2H2O and D is K2Cr2O7.
The reactions are
1. 
2. 
3. 
Thus, A is chromite of iron which when reacts with the sodium carbonate gives a yellow solution (Na2CrO4), which in the presence of the H+ ion (acid) gives compound C (Na2Cr2O7.2H2O) which on treatment with KCl solution gives orange crystal of K2Cr2O7.
OR
A is MnO2, B is K2MnO4, C is KMnO4 and D is KIO3.
The reaction involved is
1. 
2. 
3. 
Thus, the reaction involves these steps and their yields are respectively given.